From b1c33b279c6ec785b21160f3b9f05e9419f3afcc Mon Sep 17 00:00:00 2001
From: Homa Wong <homawong@gmail.com>
Date: Tue, 20 Feb 2018 13:54:31 -0800
Subject: [PATCH] feat: add onDebug overload

This support the most common usage.
---
 README.md             |  3 +++
 src/Logger.ts         |  7 +++++--
 src/getLogger.spec.ts | 15 +++++++++++++++
 src/interfaces.ts     |  8 ++++----
 4 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/README.md b/README.md
index 600ec66..852276b 100644
--- a/README.md
+++ b/README.md
@@ -35,6 +35,9 @@ log.onWarn(...)
 log.onInfo(...)
 log.onDebug(...)
 
+// or
+log.onError(() => getLogMessageThatIsTimeConsumingToCreate())
+
 function getLogMessageThatIsTimeConsumingToCreate() {
   ...
 }
diff --git a/src/Logger.ts b/src/Logger.ts
index 2f40460..9170b6c 100644
--- a/src/Logger.ts
+++ b/src/Logger.ts
@@ -50,7 +50,10 @@ export class LoggerImpl implements ALogger {
   }
 
   private on(logLevel, logFunction) {
-    if (this.level >= logLevel)
-      logFunction(this.logger[logLevelNameMap[logLevel]].bind(this.logger))
+    if (this.level >= logLevel) {
+      const logFn = this.logger[logLevelNameMap[logLevel]].bind(this.logger)
+      const result = logFunction(logFn)
+      if (result) logFn(result)
+    }
   }
 }
diff --git a/src/getLogger.spec.ts b/src/getLogger.spec.ts
index f2a4a94..384b5bb 100644
--- a/src/getLogger.spec.ts
+++ b/src/getLogger.spec.ts
@@ -267,3 +267,18 @@ test('on???() logs to corresponding log', t => {
     'error'
   ])
 })
+
+test(`pass '() => string' into on???() will log the result`, t => {
+  const log = getLogger('onXXX with () => string')
+  log.setLevel(logLevel.debug)
+  log.onDebug(() => 'debug')
+  log.onInfo(() => 'info')
+  log.onWarn(() => 'warn')
+  log.onError(() => 'error')
+  t.deepEqual(appender.logs.map(l => l.messages[0]), [
+    'debug',
+    'info',
+    'warn',
+    'error'
+  ])
+})
diff --git a/src/interfaces.ts b/src/interfaces.ts
index 76e20ad..f002503 100644
--- a/src/interfaces.ts
+++ b/src/interfaces.ts
@@ -9,8 +9,8 @@ export interface Logger extends ALogger {
   error(...args: any[]): void
   setLevel(level: number): void
 
-  onError(logFunction: (log: logMethod) => void): void
-  onWarn(logFunction: (log: logMethod) => void): void
-  onInfo(logFunction: (log: logMethod) => void): void
-  onDebug(logFunction: (log: logMethod) => void): void
+  onError(logFunction: ((log: logMethod) => void) | (() => string)): void
+  onWarn(logFunction: ((log: logMethod) => void) | (() => string)): void
+  onInfo(logFunction: ((log: logMethod) => void) | (() => string)): void
+  onDebug(logFunction: ((log: logMethod) => void) | (() => string)): void
 }